Why is Ceres special?
A dwarf planet or a huge asteroid?
The dwarf planet Ceres is the most
This orthographic projection shows the dwarf planet Ceres as seen from NASA's Dawn spacecraft.
NASA / JPL-Caltech / UCLA / MPS / DLR / IDA
Called an asteroid for yearsCeres is so much larger and so different from its rocky neighbors that scientists classified it as a dwarf planet in 2006. Although Ceres makes up 25% of the total mass of the asteroid belt, tiny Pluto is still 14 times larger and more massive.
The shortest daylight hours in the entire solar system and no seasons
Ceres needs 1682 Earth days, or 4.6 Earth daysyears to complete one revolution around the Sun. Since Ceres revolves around the Sun, it makes one revolution every 9 hours, making it one of the shortest daylight hours in the solar system.
Ceres's axis of rotation is tilted by only 4 degreesin relation to the plane of its orbit around the Sun. This means that it rotates almost perfectly vertically and is not affected by the seasons like other more inclined planets.
A germ planet that was thwarted by a neighbor
Ceres formed along with the restSolar system about 4.5 billion years ago, when gravity sucked in swirling gas and dust, turning into a small dwarf planet. Scientists describe Ceres as an “embryonic planet” - it began to form, but this process did not have time to end. The strong gravity of neighboring Jupiter prevented it from becoming a fully formed planet. About 4 billion years ago, Ceres settled in its current location among the remnants of planetary formations in the asteroid belt between Mars and Jupiter.
Is there potential for life on Ceres?
Ceres looks more like terrestrial planets(Mercury, Venus, Earth, and Mars) than its asteroid neighbors, but it is much less dense. One of the similarities is the layered structure, but the layers of Ceres are not as clearly defined. Ceres probably has a solid core and a mantle of water ice. In fact, Ceres can be 25% water. If so, there is more water on Ceres than on Earth. The bark of Ceres is stony and dusty, with large deposits of salt. Salts on Ceres are not like table salt (sodium chloride), but are composed of other minerals such as magnesium sulfate.
In this simulated perspective viewshows the Occator crater, measuring 57 miles (92 kilometers) across and 2.5 miles (4 kilometers) deep, which contains the brightest region on Ceres.
NASA / JPL-Caltech / UCLA / MPS / DLR / IDA
Ceres is covered with countless smallyoung craters, but none of them exceeds 280 kilometers in diameter. This is surprising, considering that the dwarf planet must have been hit by numerous large asteroids during its 4.5 billion year lifetime.
Lack of craters may be due to layersice just below the surface. Surface features can flatten over time if ice or other lower density material such as salt is just below the surface. It is also possible that hydrothermal activity such as ice volcanoes has erased some large craters in the past.
Some of the craters of Ceres have areas thatare always in the shadows. It is possible that water ice can remain in these "cold traps" for a long time without direct sunlight.
Ceres has a very subtle atmosphere, and there isevidence that it contains water vapor. Steam can be produced by ice volcanoes or by the sublimation of ice at the surface (solid to gas transition).
Ceres is one of the few places in our sunnya system where scientists are interested in looking for possible signs of life. Ceres has something that many other planets do not have: water. Here on Earth, water is essential for life, so it is quite possible that if this ingredient and some other conditions were present, life could exist there. Living things on Ceres, if they exist at all, are likely to be very small microbes, similar to bacteria. And while Ceres may not have living beings today, there may be signs that it had life in the past.
What did the scientists find?
NASA spacecraft "Dawn" gave scientistsunusual close-up view of the dwarf planet Ceres. By the time the mission was completed in October 2018, the orbiter had descended less than 35 kilometers above the surface, revealing clear details of the mysterious bright regions for which Ceres became known.
Scientists have found that bright areas representare deposits, consisting mainly of sodium carbonate - a compound of sodium, carbon and oxygen. Most likely, they arose from a liquid that seeped to the surface and evaporated, leaving behind a highly reflective salt crust. But they have not yet determined where this liquid came from.
After analyzing the data collected near the endmission, the scientists of the Dawn mission concluded that the liquid came from a deep reservoir of "brine" or salt-enriched water. By studying Ceres' gravity, scientists have learned more about the inner structure of the dwarf planet and were able to determine that the brine reservoir is about 40 kilometers deep. Its width is hundreds of kilometers.
Ceres does not benefit from internal heating,caused by gravitational interaction with a large planet, as is the case with some icy moons in the outer solar system. But new research, which focuses on Ceres' 92 km occatorial crater, home to the most expansive bright regions, confirms that Ceres is a water-rich world like these other ice bodies.
This mosaic image uses a falsecolor to highlight newly exposed brine or salty liquids that have pushed out of a deep reservoir beneath Ceres's crust. They appear reddish in this image of the Occator crater area.
Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA
The results, which also show the degree of geological activity in Occator Crater, were published on August 10 in the journals Nature Astronomy, Nature Geoscience and Nature Communications.
Dawn has accomplished much more than ushoped when she embarked on her unusual extraterrestrial expedition. These exciting new discoveries at the end of a long and productive mission are a wonderful tribute to this remarkable interplanetary explorer.
Mission director Mark Rayman of NASA's Jet Propulsion Laboratory in Southern California.
This mosaic of the Occator crater on Ceres consists ofimages captured by NASA's Dawn mission during its second extended mission in 2018. The bright pits and hills (in the foreground) were formed by the salty fluid released when Occator's water-rich floor froze over after a crater-forming impact. about 20 million years ago.
NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / USRA / LPI
Observations of astronomers before "Dawn"
Long before the Dawn mission arrived atCeres in 2015, scientists noticed diffuse bright areas in telescopes, but their nature was unknown. From its close orbit, Dawn snapped images of two separate, highly reflective regions in Occator Crater, which were later named Cerealia Facula and Vinalia Faculae (Faculae means light areas).
Scientists knew that micrometeorites often attacksurface of Ceres, causing bumps and debris. Over time, doing this should darken these bright areas. Thus, their brightness indicates that they are probably young. Trying to understand the source of the regions and how the material could be so new was the main goal of the last Dawn Expanded mission from 2017 to 2018.
The study not only confirmed that brightthe sites are young—some are less than 2 million years old. Also, thanks to the mission, scientists discovered that the geological activity leading to the appearance of these deposit sites may continue.
On the surface of Ceres, salts that carry water quicklydehydrate over hundreds of years. But measurements from the Dawn mission show they still have water in them, so the fluids must have reached the surface quite recently. This indicates both the presence of liquid below the region of the Occator crater and the ongoing transfer of material from deep depths to the surface.
Scientists have discovered two main pathways by which fluids can reach surfaces.
For a large deposit in CerealiaFacula, the bulk of the salts came from slush just below the surface, which was melted by the heat of the impact that created the crater about 20 million years ago. The effects of heat subsided after a few million years; however, the impact also created large cracks that could reach the deep, long-lived reservoir, allowing brine to continue to seep to the surface.
Carol Raymond, Dawn Mission Principal Investigator
Active geology: recent and unusual
In our solar system, icy geologicalactivity occurs primarily on icy moons, where it is driven by their gravitational interaction with their planets. But this is not the case for the movement of brines to the surface of Ceres, which suggests that other large ice-rich bodies that are not moons may also be active.
Some evidence of fluid movement inOccator Crater is exposed by bright deposits on the surface, but other clues come from a large number of interesting conical mounds that resemble pingos on Earth - small ice mountains in the polar regions formed by frozen groundwater under pressure. Such features have been seen on Mars, but their discovery on Ceres marks the first time they have been observed on a dwarf planet.
On a larger scale, scientists were able to imageDensity of Ceres crustal structure as a function of depth — a first for an ice-rich planetary body. Using gravity measurements, they found that the density of Ceres' crust increases significantly with depth, beyond simple pressure effects. The researchers concluded that as Ceres' reservoir freezes, salt and silt seep into the lower crust.
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